Table 5 Hierarchy of evidence
Level of evidenceType of evidence
IaEvidence from systematic reviews or meta-analysis of randomised controlled trials
IbEvidence from at least one randomised controlled trial
IIaEvidence from at least one controlled study without randomisation
IIbEvidence from at least one other type of quasi-experimental study
IIIEvidence from non-experimental descriptive studies such as comparative studies, correlation studies and case-control studies
IVEvidence from expert committee reports or opinions and/or clinical experience of respected authorities